This invention relates to pressure and/or heat applied image transfersxe2x80x94this includes rub-down image transfers, but rubbing down is not the only method of transferring the image from the image carrier to the target surface.
Rub-down image transfers are well-knownxe2x80x94the system sold under the trade name xe2x80x9cLetrasetxe2x80x9d will be very familiar, which appears as sheet with various indicia including letters and numerals in different type faces which can be transferred from the face of the sheet on to the target surface (e.g. a drawing on paper) by placing the image face against the paper and rubbing down or burnishing the back of the sheet so that the letter or numeral becomes attached to the target surface and detached from the sheet.
There have been several attempts to extend this process into full colour reprographics, and such attempts have involved more or less complicated procedures and the use of particular materials with some limitations as to the nature of the final target surface, all at considerable cost, in terms of both materials cost and processing cost and complexity.
The present invention provides methods for preparing a pressure and/or heat applied image transfer sheet, and such sheets, which are less expensive and easier to use, with superior results, as compared to prior art techniques. The methods are applicable to a wide range of target surfaces, including compact discs and leather items. Furthermore, the methods can be adapted for use in mass production applications.
The invention comprises a method for preparing a pressure and/or heat applied image transfer sheet and applying an image therefrom to a target surface comprising:
applying an image layer to an image area of an image release system on a support, the image release system comprising an image release surface;
applying a pressure-activated and/or heat activated adhesive layer over i) the image release system including the image area and/or ii) at least a portion of the target surface, which adhesive layer adheres more strongly to the image layer than the image layer does to the release surface;
contacting, with the application of pressure and/or heat, the target surface and the image transfer sheet such that the dried adhesive layer attaches only in the image area to i) the target surface and/or ii) the image transfer sheet;
and peeling off the support together with the adhesive layer except for the image area which is left attached to the target surface.
The method may comprise:
applying a pressure and/or heat activated adhesive layer over the image release system including the image area;
such that when the dried adhesive layer is applied to a target surface with the application of pressure and/or heat it attaches to the target surface only in the image area but is otherwise retained by the support.
Alternatively, the method may comprise:
applying a pressure and/or heat activated adhesive layer over at least a portion of the target surface;
contacting, with the application of pressure and/or heat, the target surface and the image transfer sheet such that the dried adhesive attaches only in the image area to the image transfer sheet.
The release surface may be on a film support layer which is itself attached to a backing by a release coat on a backing adhesive coat of the backing, the backing being first peelable from the support so as to leave the image visible through the film.
The image layer may be applied using a dry toner medium, or an ink or a paint. The image may be masked with a white pigment.
The image may be applied using a dry toner electrophotographic process (xerography) or an electroink printing process (e.g. the Indigo (trademark) process).
White pigment masking, in xerography may be by way of a white pigment foil; in electroink printing, a white pigment ink may be used.
The purpose of the white pigment masking is threefoldxe2x80x94first, it allows pastel shades to be properly represented, it protects the image, which would otherwise be exposed and liable to damage, second it creates opacity.
The image may be masked with a metallised foil.
The image may be masked with a holographic element.
The image release system may bind the image layer to the image release surface with an interfacial tension of 38-39 dynes/cm2, or may be surface treated, as by a corona discharge treatment, to attain a suitable surface tension, though corona treatment tends to apply only a temporary effect.
The adhesive layer may be applied just prior to application to the contacting of the target and the image transfer sheet. It may be applied by spraying or by roller coating, when organic solvent based adhesives will be found suitable, or it may be applied by means of an adhesive sheet, in which the adhesive may be water-based.
The image release system may bind the adhesive layer to the image release surface with a surface tension 4-5 dynes/cm2 less than that which it binds the image layer to the image release surface.
The image release system may bind the adhesive layer to the image release surface with a surface tension of 34 dynes/cm2.
The adhesive may be activated solely by heat and is desirably fast drying so that application to the target surface is not delayed too long after application of the adhesive.
Application of pressure to transfer the image to the target surface may be by means of a pressure roller, which may be used hot or cold, by a plate, as in foil blocking, or by burnishingxe2x80x94fingers may suffice, but burnishing tools capable of applying higher, more localised pressure will usually be preferred.
The target surface may comprise a surface of a compact disc, in which instance the adhesive layer may be applied over the entire surface of the compact disc or one or more selected portions of the surface of the compact disc.
Images may be transferred to a plurality of target surfaces. These target surfaces may comprise the surfaces of objects positioned on a moveable web, and the image transfer sheet may comprise a web having a plurality of image areas, the web being fed by rollers so as to contact the target surfaces. The adhesive layer may be applied to the web which has a plurality of image areas.
The target surface may comprise glass, plastic, fabric, wood or leather.
The invention also comprises an image transfer system comprising a pressure and/or heat applied image transfer sheet comprising an image release system on a support, the image release system comprising an image release surface and adapted to receive an image layer on any part of the image release system (the image area) which image layer is releasably held on said surface, and a pressure activated adhesive to be applied after the image to the image release system including the image area and/or at least a portion of a target surface and having the characteristic that it binds more firmly to the image layer than the image layer binds to the image release surface and intended for application to a target surface to which it binds less firmly than to the image release surface.
The release surface may be on a film support layer which is itself attached to a backing (such as, conveniently, paper or a synthetic material) by a release coat on a backing adhesive coat of the backing, the backing being first peelable from the support so as to leave the image visible through the film.
The film may be a polyester, which may be of polyethylene terephlthate (PET), or polyethylene naphthalate (PEN). Alternatively, the film may be polypropylene (OPP).
The image release surface may be a release coating on the support, which may comprise a wax coating.
The image release system may comprise at least one differential binding layer located over the image release surface. The differential binding layer may be a lacquer.
The surface may be corona discharge treated, however, and may have a surface tension to an applied image of 38-39 dynes/cm2.
The image release system may bind the adhesive layer to the image release surface with a surface tension 4-5 dynes/cm2 less than that at which it binds the image layer to the image release surface.